"If my theory of relativity is proven successful, Germany will claim me as a German and France will declare that I am a citizen of the world. Should my theory prove untrue, France will say that I am a German and Germany will declare that I am a Jew." - Albert Einstein ( 1879 - 1955 )

"It followed from the special theory of relativity that mass and energy are both but different manifestations of the same thing -- a somewhat unfamiliar conception for the average mind. Furthermore, the equation E is equal to m c-squared, in which energy is put equal to mass, multiplied by the square of the velocity of light, showed that very small amounts of mass may be converted into a very large amount of energy and vice versa. The mass and energy were in fact equivalent, according to the formula mentioned above. This was demonstrated by Cockcroft and Walton in 1932, experimentally." - Prof. Albert Einstein ( excerpts from 1947 film, "Atomic Physics" )

Special Relativity physics was first published in 1905 by Albert Einstein at age 26 working quietly in the Swiss Patent Office, Bern, Switzerland, under the title "On The Electrodynamics Of Moving Bodies", translated from "Zur Elektrodynamik bewegter Körper", Annalen der Physik, volume 17: 891, Bern June 1905, a downloadable copy of which is available here in pdf. German version: "Zur Elektrodynamik bewegter Körper", von A. Einstein.

However the entire classical Newtonian physics derived above is predicated upon the concept of mass as an invariant constant. But we now know differently, namely that mass is a speed - dependent variable quantity owing to the Addition of Relativistic Velocities, where

is the relationship between rest ( or proper ) mass undergoing velocity and its equivalent dilated mass .

§ More Definitions:

inertial mass is the invariant rest ( or proper, co - moving ) mass when and is a quantitative measure of a non - accelerating body's resistance to acceleration. It is furthermore considered as "reserve" potential energy; or quoting Einstein, "... that inert mass is simply latent energy".

However, Hasenöhrl's derivation was an entirely classical derivation in the manner of Newton and James Clerk Maxwell without the overall context of relativistic physics which Einstein brought into full fruition by his 'principle of relativity' mathematics.

The other couple of lines of intellectual attack against Einstein for his relativistic understanding of the inertial mass of all electromagnetic energy propagation arose first by Nazi Nobelist Philipp Lenard in his anti - semitic Deutsche Physik movement by which Lenard attempted to ascribe special relativity credit away from Jewish Albert Einstein and onto Johann Georg von Soldner and Paul Gerber but was immediately and totally rebutted by Max von Laue, recipient of the Nobel Physics Prize in 1914 for the diffraction of x - rays by crystals; and whereas the second line of attack arose by those who supported Henri Poincaré's mathematics which, however, ultimately lacked the fullness of the intimate nexus of space-with-time that Einstein's special relativity physics provided and wholly elaborated upon in the light - sphere geometry of "Space and Time", by Hermann Minkowski, Cologne 1908. Hence, Poincaré's mathematics was "pre - relativistic", he having discovered the few remaining Lorentz velocity transformations still outstanding including those for Maxwell's electromagnetic equations. Read: "On The Dynamic of the Electron", by Henri Poincaré, 1905, English translation.

Einstein abjured as late as his 1934 Gibbs Lecture at the Carnegie Institute of Technology ( now Carnegie - Mellon University ) the well established, modern consensus for the concept of "speed - dependent" mass otherwise known as "relativistic mass" when he continued to insist on writing 'mass' as an invariant scalar ( tensor rank zero ) as follows:

as opposed to the modern relativistic physics of

That Einstein maintained such an interpretation is amply shown in the following couple of theses:

§ [1] Caveat:The name 'Einstein' in the above passages of this web page essay is to be understood more generally as encompassing the mathematical works of Max Planck, especially as regards "relativistic mass" which

Einstein himself avoided in favor of inertial or, equivalently, rest ( proper ) mass, as revealed above in the Epilogue: Some Final Questions, particularly regarding the question "...as to what meaning did Einstein